Optical device and method for its fabrication

Abstract

An optical device comprising: a quantum dot, said quantum dot comprising InAs and adapted to emit radiation in the wavelength range from 1200 nm to 2000 nm; a supporting layer supporting said quantum dot, said supporting layer being lattice matched to InP; and wherein the longest dimension of the base of the quantum dot provided parallel to the supporting layer is within 20% of the shortest dimension of the base provided parallel to the supporting layer.

1 . An optical device comprising:
 a quantum dot, said quantum dot comprising InAs and adapted to emit radiation in the wavelength range from 1200 nm to 2000 nm;   a supporting layer supporting said quantum dot, said supporting layer being lattice matched to InP; and   wherein the longest dimension of the base of the quantum dot provided parallel to the supporting layer is within 20% of the shortest dimension of the base provided parallel to the supporting layer.   
     
     
         2 . An optical device according to  claim 1 , wherein the fine structure splitting of the quantum dot is 50 μeV or less. 
     
     
         3 . An optical device according to  claim 1 , comprising a (100) oriented substrate. 
     
     
         4 . An optical device according to  claim 1 , further comprising a wetting layer provided overlying the supporting layer. 
     
     
         5 . An optical device according to  claim 4 , wherein the supporting layer comprises InP or InGaAsP. 
     
     
         6 . An optical device according to  claim 5 , wherein the wetting layer comprises InAsP. 
     
     
         7 . An optical device according to  claim 1 , wherein the supporting layer comprises AlInAs or AlInGaAs. 
     
     
         8 . An optical device according to  claim 1 , wherein an upper layer is provided overlying the quantum dot. 
     
     
         9 . An optical device according to  claim 1 , comprising a plurality of quantum dots, and wherein the density of the quantum dots is less than 1×10 9 cm −2 . 
     
     
         10 . An optical device according to  claim 1 , configured as an LED comprising an n doped region provided on one side of the quantum dot and a p doped region on the other side of the quantum dot. 
     
     
         11 . An optical device according to  claim 4 , further comprising a filter, said filter being adapted to filter out radiation emitted by the wetting layer. 
     
     
         12 . An optical device according to  claim 1  comprising a cavity region, said cavity region adapted to accommodate said quantum dot and preferentially reflect radiation emitted from said quantum dot within said cavity. 
     
     
         13 . An optical device according to  claim 12 , wherein the cavity is an asymmetric cavity comprising a single distributed Bragg reflector provided on one side of the cavity. 
     
     
         14 . An optical device according to  claim 12 , wherein the cavity comprises an intrinsic region and a p-doped region is provided on one side of the quantum dot, the thickness of the layers between the quantum dot and the p-doped region being greater than the distance over which the p-type dopants diffuse into the intrinsic region at the growth temperature of the device. 
     
     
         15 . An optical device according to  claim 1 , wherein the support layer is patterned and the quantum dot is positioned at point in the pattern. 
     
     
         16 . A method of fabricating an optical device, the method comprising:
 forming a support layer, said support layer being lattice matched to InP;   forming a layer of In, said amount of In being controlled to allow the formation of In droplets;   growing As over said In droplets and crystallising said droplets to form InAs dots;   wherein the formation of the In droplets and crystallisation is controlled to produce quantum dots adapted to emit radiation in the wavelength range from 1200 nm to 2000 nm and wherein the longest dimension of the base of the quantum dot provided parallel to the supporting layer is within 20% of the shortest dimension of the base provided parallel to the supporting layer.   
     
     
         17 . A method of fabricating an optical device according to  claim 16 , wherein the layers are formed using MOVPE or MBE 
     
     
         18 . A method of fabricating an optical device according to claim le wherein the structure is formed using MOVPE and 2ML of In is deposited to form the droplets. 
     
     
         19 . A method of fabricating an optical device according to  claim 16 , wherein the growth temperature is raised as the As is grown over the In droplets. 
     
     
         20 . A method of fabricating an optical device according to  claim 16 , wherein the droplets are capped immediately after the As is grown.